Satellite communications systems and methods are widely used for wireless communications. Satellite communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is configured to wirelessly communicate with a plurality of satellite radioterminals.
A satellite radioterminal communications system or method may utilize a single antenna pattern (beam or cell) covering an entire area served by the system. Alternatively or in combination with the above, in cellular satellite radioterminal communications systems and methods, multiple antenna patterns (beams or cells) are provided, each of which can serve substantially distinct geographical areas in the overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular/PCS radioterminal systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radioterminals over a bidirectional communications pathway, with radioterminal communications signals being communicated from the satellite to the radioterminal over a downlink or forward link, and from the radioterminal to the satellite over an uplink or return link.
The overall design and operation of cellular satellite radioterminal systems and methods is well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radioterminal” includes cellular and/or satellite radioterminals with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet/Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “radioterminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth and/or in space. A radioterminal also may be referred to herein as a “radiotelephone,” “terminal”, or “wireless user device”. As used herein, the term “space-based” component includes one or more satellites and/or one or more other objects/platforms (e.g., airplanes, balloons, unmanned vehicles, space crafts, missiles, etc.) that have a trajectory above the earth at any altitude. Furthermore, as used herein, the term “transmitting/receiving data” shall have the same meaning and may be used interchangeably with the term “transmitting/receiving information.”
A terrestrial network can enhance an availability, efficiency and/or economic viability of a cellular satellite radioterminal system by terrestrially using/reusing at least some of the frequencies that are authorized for use and/or are used by the cellular satellite radioterminal system. In particular, it is known that it may be difficult for cellular satellite radioterminal systems to reliably serve densely populated areas, because satellite signals may be, for example, blocked by high-rise structures and/or may not penetrate into buildings. As a result, satellite spectrum may be underutilized or unutilized in such areas. Terrestrial use/reuse of at least some of the satellite system frequencies can reduce or eliminate this potential problem.
A capacity of a hybrid system, comprising terrestrial and satellite-based communications, configured to terrestrially use/reuse at least some of the satellite-band frequencies, may be higher than a corresponding satellite-only system since terrestrial frequency reuse may be much denser than that of the satellite-only system. In fact, capacity may be enhanced where it may be mostly needed, i.e., in densely populated urban/industrial/commercial areas where the signal(s) of a satellite-only system may be unreliable. As a result, a hybrid (satellite/terrestrial cellular) system that is configured to use/reuse terrestrially at least some of the frequencies of the satellite band may become more economically viable, as it may be able to serve more effectively and reliably a larger subscriber base.
One example of terrestrial reuse of satellite band frequencies is described in U.S. Pat. No. 5,937,332 to the present inventor Karabinis entitled Satellite Telecommunications Repeaters and Retransmission Methods, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described therein, satellite telecommunications repeaters are provided which receive, amplify, and locally retransmit the downlink/uplink signal(s) from satellite(s)/radioterminal(s) thereby increasing an effective downlink/uplink margin in the vicinity of the satellite telecommunications repeaters and allowing an increase in the penetration of uplink and downlink signals into buildings, foliage, transportation vehicles, and other objects which can reduce link margin. Both portable and non-portable repeaters are provided. See the abstract of U.S. Pat. No. 5,937,332.
Satellite radioterminals for a satellite radioterminal system or method having a terrestrial communications capability by terrestrially using/reusing at least some of the satellite frequency band and using substantially the same air interface for both terrestrial and satellite communications may be more cost effective and/or aesthetically appealing than other alternatives. Conventional dual band/dual mode radioterminal alternatives, such as the well known Thuraya, Iridium and/or Globalstar dual mode satellite/terrestrial radioterminals, duplicate some components (as a result of the different frequency bands and/or air interface protocols that are used for satellite and terrestrial communications), which can lead to increased cost, size and/or weight of the radioterminal. See U.S. Pat. No. 6,052,560 to the present inventor Karabinis, entitled Satellite System Utilizing a Plurality of Air Interface Standards and Method Employing Same.
U.S. Pat. No. 6,684,057, to present inventor Karabinis, and entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein, describes that a satellite frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. In particular, a system according to some embodiments of U.S. Pat. No. 6,684,057 includes a space-based component that is configured to receive wireless communications from a first radiotelephone in a satellite footprint over a satellite radiotelephone frequency band, and an ancillary terrestrial network that is configured to receive wireless communications from a second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. The space-based component also receives the wireless communications from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band as interference, along with the wireless communications that are received from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. An interference reducer is responsive to the space-based component and to the ancillary terrestrial network that is configured to reduce the interference from the wireless communications that are received by the space-based component from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band.
Satellite radioterminal communications systems and methods that may employ terrestrial use/reuse of satellite frequencies by an Ancillary Terrestrial Network (ATN) comprising at least one Ancillary Terrestrial Component (ATC) are also described in Published U.S. Patent Application Nos. US 2003/0054760 to Karabinis, entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum; US 2003/0054761 to Karabinis, entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies; US 2003/0054814 to Karabinis et al., entitled Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0073436 to Karabinis et al., entitled Additional Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0054762 to Karabinis, entitled Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems and Methods; US 2003/0153267 to Karabinis, entitled Wireless Communications Systems and Methods Using Satellite-Linked Remote Terminal Interface Subsystems; US 2003/0224785 to Karabinis, entitled Systems and Methods for Reducing Satellite Feeder Link Bandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 to Karabinis et al., entitled Coordinated Satellite-Terrestrial Frequency Reuse; US 2002/0090942 to Karabinis et al., entitled Integrated or Autonomous System and Method of Satellite-Terrestrial Frequency Reuse Using Signal Attenuation and/or Blockage, Dynamic Assignment of Frequencies and/or Hysteresis; US 2003/0068978 to Karabinis et al., entitled Space-Based Network Architectures for Satellite Radiotelephone Systems; U.S. Pat. No. 6,785,543 to Karabinis, entitled Filters for Combined Radiotelephone/GPS Terminals; US 2003/0153308 to Karabinis, entitled Staggered Sectorization for Terrestrial Reuse of Satellite Frequencies; and US 2003/0054815 to Karabinis, entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns In Response to Terrestrial Reuse of Satellite Frequencies, all of which are assigned to the assignee of the present invention, the disclosures of all of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Some satellite radioterminal communications systems and methods may employ satellites that use multiple bands for communications with radioterminals. For example, U.S. patent application Publication Ser. No. US 2003/0054762 to Karabinis, cited above, describes satellite radioterminal systems and communications methods that include a space-based component that is configured to communicate with radioterminals in a satellite footprint that is divided into satellite cells. The space-based component is configured to communicate with a first radioterminal in a first satellite cell over a first frequency band and/or a first air interface, and to communicate with a second radioterminal in the first or a second satellite cell over a second frequency band and/or a second air interface. An ancillary terrestrial network also is provided that is configured to communicate terrestrially with the first radioterminal over substantially the first frequency band and/or substantially the first air interface, and to communicate terrestrially with the second radioterminal over substantially the second frequency band and/or substantially the second air interface. See the Abstract of U.S. Patent Application Publication No. US 2003/0054762.